From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Tue, 9 Jan 2018 11:31:04 +0100
Subject: softirq: keep the 'softirq pending' check RT-only
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 5536f5491a2e098ba34995662dfc0e82d66d65c9
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

The patch "nohz: Prevent erroneous tick stop invocations" was merged
differently upstream. The original issue where a slow box could lock up
with a pending timer remained. I currently assume that this is a RT only
issue and keep the patch as RT only.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 kernel/softirq.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -839,8 +839,13 @@ static inline void tick_irq_exit(void)
 	int cpu = smp_processor_id();
 
 	/* Make sure that timer wheel updates are propagated */
+#ifdef CONFIG_PREEMPT_RT_BASE
 	if ((idle_cpu(cpu) || tick_nohz_full_cpu(cpu)) &&
-	    !need_resched() && !local_softirq_pending()) {
+	    !need_resched() && !local_softirq_pending())
+#else
+	if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu))
+#endif
+	{
 		if (!in_interrupt())
 			tick_nohz_irq_exit();
 	}